Zein solution and coating composition



Patented Dec. 26, 1939 zen: sow-non AND coA'rrNG COMPOSITION Roy E.Coleman, Chicago, Ill., assignor to The zein Corporation of America, acorporation of Delaware No Drawing. Original application September 21,

1939, Serial No. 295,919. Divided and this application October 11, 1939,Serial No. 298,991

9 Claim.

This invention relates to improvements in substantially anhydroussolutions and coating compositions of zein and to methods of preparingthe same. While the present invention is applicable to the production 01solutions and coating compositions of other prolamins, it isparticularly directed to securing substantially anhydrous solutions andcoating compositions of zein with controlled solution and gellingcharacteristics,

zein being difierentiated from other prolamins by its'unusual gellingtendencies.

This application is a division of my prior copending application SerialNo. 295,919, filed September 21, 1939.

The solutions and coating compositions of my present invention arecharacterized by the fact that they contain either no added ,water oronly very slight amounts of water not in excess of about 5% and are,therefore, substantially anhydrous.

The zein used in accordance with my invention may be the commercial zeinwhich contains a small percentage of moisture in the order of about 5 toabout'8%, preferably about 8%, and is ob- 25 tained in the trade inpowdered form, or it may be a specially treated substantially anhydrouszein. In the following description of my invention I refer by the termzein to commercial zein or to zein of substantially the water content of30 commercial zein unless otherwise specifically designated.

In the prior art zein coating compositions, water has been included to asubstantial extent, it being considered that the solubilitycharacteristics of 35 zein required the inclusion of substantialproportions of water in organic solvents. For example, as stated in theWalsh et a1. Patent No. 1,966,604, the addition of water is necessarysince the lowmolecular weight alcohols, alcohol ethers and al- 40 coholderivatives are not effective alone in making solutions of zein.

In accordance with the present invention I have found thatnon-separating, stable liquid coating compositions of controlled gellingchar-- 45 acteristics, either slow-gelling or substantially non-gelling,can be prepared from zein by the aid of anhydrous or substantiallyanhydrous solvents or mixturesof such solvents. These coatingcompositions, over wide range of concen- 50 trations, are stable onstanding at temperatures of 80 F. and below and do not separate evenwhen cooled to temperatures of 50 to 70 F. and somewhat below. Whencooled even to temperatures as low as 10 above zero or to zero, solu- 55tions or coatings repared in accordance with the (01. lei-12) presentinvention may separate and become solid; however, on heating again totemperatures of from 45 to 70 F'., a re-solution is effected, eitherwithout stirring or with slight stirring, and the solutions and coatingsreturn to their normal form 5 at the re-heating temperatures.

The stable non-separating solutions and coating compositions prepared inaccordance with the present invention may be controlled 'as to theirgelling characteristics, as hereinafter set 10 forth, and may beslow-gelling or substantially non-gelling with slight tendency toincrease in viscosity; that is, to thicken or become heavier in body;and in many instances they exhibit practically no tendency to thicken orto gel over practical periods of time in the orderof about 3 to about 6months. By virtue of these novel stable characteristics, the solutionsand coatings of my invention are not limited to use immediately orwithin short periods of time after preparation as is generally the casewith the prior art solutions and coating compositions. The solutions andcoating compositions of the present invention generally remain stableand reasonably constant in their characteristics during the periods;necessary for transportation and distribution, either in bulk or inpackages, or for storage for reasonable periods of time, and hence theirfield of applicability is greatly increased.

In accordance with-the present invention, I have found that solutionsand coatings of zein having the desired non-separating, controlledgelling or non-gelling characteristics may be secured by a suitablebalance between the hydrocarbon constituents or radicals present in thesolvent or 501- vent mixtures and the polar constituents or radicalspresent therein, the presence of a certain proportion of carbon-bondedhydroxyl radicals being required to secure solvent action. The presenceof a hydroxyl group in a primary alcohol radical, CHzOH, appears to beparticularly helpful in securing such action. The presence of anexcessive proportion of hydroxyl radicals or of polar radicals includingsome hydroxyl radicals causes or accelerates gelling tendencies in thezein solution or coataing. Polar radicals such as O-- (ether oxygen),Cl, -NH2, =CO and COOH thus appear to aid or cooperate with OI-I insecuring the necessary conditions of polarity in the solver itflin whichterm I include solvent mixtures in the present case) for solvent action,and in excess produce the conditions enhancing gelling. While insolutions absence of gelling or slow-gelling or thickening is desirable,in the preparation of plastics rapid gelling may be desirable. In thepresent case I am more particularly concerned with solutions havingslow-gelling or substantially non-gelling characteristics for use incoating compositions; i. e., solutions which do not gel or which gel orthicken so slowly as to permit normal commercial handling withoutmaterial or serious thickening or gelling.

The proportion of" hydrocarbon or non-polar radicals in the solvent orsolvent mixture should not be excessive, since too high a proportion ofhydrocarbon apparently causes insolubility and separation of the zein.The same is the case in the presence of excessively long or largehydrocarbon radicals; e. g., C4 and higher alkyl radicals. Cyclichydrocarbon radicals, however, behave as lower alkyl radicals. Thus, aswill appear hereinafter, the benzyl radical acts as if it wereintermediate between the methyl and ethyl radicals. This is consistentwith the polar characteristics of aryl-alkyl radicals as compared withalkyl-alkyl radicals.

The desired balance of polarconstituent radicals and hydrocarbon ornon-polar radicals in the solvent may be secured by the use of asuitable as individual compound which inherently has the necessarybalance, or by an admixture of com pounds which are individually notbalanced to secure proper relations in the mixture and whichindividually may not be solvents for zein. The behavior of such mixturesmay be explained by assuming solvation of the zein molecules or micellesby the hydroxylated constituents of the mixture, with orientation of thehydrocarbon radicals of the hydroxylated compoundto the exterior of thesolvate complex, which may then disperse or dissolve in the remainingconstituents of the solvent.

The proportion of polar radicals to hydrocarbon or non-polar radicalswhich I have found to be desirable lies within a range which extendsbetween the limits of absolute methanol on the one hand, having 53%hydroxyl and 47% hydrocarbon, and absolute ethanol on the other handhaving 37% hydroxyl and 63% hydrocarbon. This range is approximate andmay vary somewhat depending on the solvent or solvent mixture used. Thelimits of this range are, however, in-

dicative of gelling characteristics on the one hand and of insolubilityon the other and, therefore, provides a close and adequate guide toenable the operator, by simple experimentation to determine the requiredbalance of polar and hydrocarbon radicals to effect solution of zeininany solvent or mixture of solvents of a character herein set forth. Thusabsolute methanol has decided solvent action, but has excessive gellingtendencies, as has also ethylene glycol, which has an even higherproportion of .OH than has methanol. Glycerol, also higher in --OH thanmethanol, shows no appreciable solvent action on zein, a behavior whichis probably related to its high surface tension. On the other hand,absolute ethanol, isopropanol, and higher alcohols have no apparentsolvent action.

It is, of course, obvious that certain solvents or mixtures of solventshaving a balance of polar and hydrocarbon radicals within the limitsabove set forth will produce solutions or coatings which are moresuitable for special commercial purposes than other balanced solvents-or balanced mixtures of solvents. By using the criticalpolarhydrocarbon radical balance range as a guide, it is possible, bysimple experimentation, to determine readily that particular balancedsolventor balanced mixture of solvents which will produce and ethanol.

the solution or coating composition having the desired properties andcharacteristics for the special purpose.

Various relatively high molecular weight alcohols, having a ratio ofpolar to non-polar radicals between methanol and ethanol are excellentindividual solvents for zein with the production of non-gelling,non-separating solutions and coatings, as set forth in my priorapplications Serial No. 187,559; Serial No. 187,560; and Serial No.

188,182, which were filed as continuations-in-part of application SerialNo. 158,215. The solvents of these applications include diethyleneglycol, triethylene glycol, propylene glycol, diacetone alcohol, benzylalcohol, cyclohexanol and furfuryl alcohol, as well astetrahydrofurfuryl alcohol and the like. These solvents are capable ofdissolving zein to produce solutions or coating compositions which arestable againstseparatlon and are controlled to be slow-gelling orsubstantially non-gelling over practical periods of time; in many casesover from about 3 to about 6 months. In Examples 1 to 8 of my priorapplication Serial No. 295,919, I disclose methods of preparing zeinsolutions by the aid of these individual solvents.

Considering the cyclic and aryl-alkyl radicals of the compounds benzylalcohol, cyclohexanol, furfuryl and tetrahydrofurfuryl alcohols asintermediate between the CH3 and the CH3CH2-- radicals, it will be notedthat in all of these solvents the proportion of polar radicals (-OH orOH and O) may be regarded as if it were intermediate between the ratiosfor methanol I have found that any of the above balanced solvents ormixtures of them may be used in or added to other solvents or solventmixtures, otherwise balanced or approximately balanced, such additionsbeing frequently desirable. Thus, benzyl' alcohol aids in securing ahydroxyl and other polar groups to hydrocarbon radicals is maintainedwithin the proper balance,

as set forth in Examples 9 'to 24 of my prior application Serial No.295,919.

Solvent mixtures of non-gelling or controlled gelling characteristicsmay be produced by mixing compounds, each having the desired balance ofpolar and hydrocarbon radicals as in Examples 25 to 29 of my applicationSerial No. 295,919.

Solvent mixtures of non-gelling or controlled gelling characteristicsmay be produced by mixing miscible compounds having a deficiency ofhydroxyl or polar radicals with compounds having a balance or an excessthereof to secure the desired balance of polar'and hydrocarbon radicalsin the resulting mixtures. An extreme example of the production of suchsolvents is the admixture of toluene (a non-solvent for zein) andmethanol. Mixtures of methanol and toluol containing 5 to 45% of toluolare excellent solvents for zein, and have retarded and in some casesrelatively slow-gelling tendencies. The preferred range is 35 to 45%toluol. Examples 30 to 34 of my prior application Serial No. 295,919 areillustrative of such mixtures.

Anhydrous or substantially anhydrous solvents may be prepared'from thealiphatic alcohols having from '2 to 4 carbon atoms by adding theretohydroxylated or polar compounds having higher ratios of 0H or polargroups (in-.

simplest monoand polyhydric alcohols are particularly useful in thisconnection, these being methanol, glycol and glycerol. Examples to 41 ofmy prior application Serial No. 295,919 are illustrative of zeinsolutions prepared with such solvent mixtures.

Certain anhydrous or substantially anhydrous compounds or mixtures ofcompound in accordance with the present invention, characterized inhaving a balance of polar and hydrocarbon radicals approaching that ofethanol and bordering the desired range, have been found to be excellentsolvents for zein. Solutions or coating compositions formed by the aidof these solvents are stable against separation of the zein and producesolutions in which the gelling tendencies can be more readily controlledthan in the case of solutions or coating compositions formed by the aidof these solvents and substantial amounts of water as in the prior art.01" the solvents, mention may be made of ethylene glycol monomethylether, diethylene glycol monomethyl ether, ethylene glycol monoethylether, diethylene glycol monoethyl ether and like alcohol-ether solventsor mixtures thereof. The following examples are illustrative ofsolutions prepared with these solvents. In the examples, the term partsindicates parts by weight.

Example 1 10 parts of zein are mixed with parts of ethylene glycolmonomethyl ether in a suitable vessel. On stirring the mixture at roomtemperature (about 73 F.) for about 3 to 4 minutes, the zein isconverted into a viscous, translucent, semi-plastic mass. On continuedstirring for about 1 to 6 minutes, a clear, bright, strawcolored,non-separating slow-gel ing, stable solution of the zein in the solventis obtained.

Example 2 Example 3 10 parts of zein are mixed with 40 parts of ethyleneglycol monoethyl ether. The mixture mixes well at room temperature butdoes not quickly dissolve. On stirring for about 5 minutes and with theapplication of heat in the order of 95 to 100 F. the zein begins to gointo solution. On continued stirring for about 5 to 10 minutes and withthe further application of heat in the order of 110 to 125 F., a clear,bright, non-separating slow-gelling, stable solution of the zein isproduced.

The solvents and solvent mixtures for zein set forth above and theresulting solutions prepared in accordance with the present inventionare substantially anhydrous, containing not more than 5% of added waterand, preferably, substantially less. The proportions of waterpermissible are thus limited in order to secure the desired solutioncharacteristics and control of gelling, since it has been found that thepresence of water in excess of the proportions aboveindicated disturbsthe balance of the solvent, tending to produce or to accelerate gelling,as well as to impair the character of the zein film deposited from thesolution. Possible explanations of the behavior of water may be made onthe basis that it acts as a highly polar constituent when present insolution in excess, that it tends to cause solvation or hydration of thezein, and its tendency to cause gelling may also be related to itshigh'surface tension. The permissible.proportion may vary in varioussolvents or solvent mixtures, the maximum permissible being representedby the permissible proportion of 5% in the case of ethyl alcohol or theethyl alcohol constituent of the solvent. with 5% water is a solventproducing stable solution in only limited cases, as set forth in myapplication Serial No. 158,215, and in all otherinstances is but oneconstituent of a mixture, it will be apparent that the solvents preparedin accordance with the present invention contain (except in thosespecific instances) substantially less than 5% of added water.

The extent of the effect of water and the permissible proportion thereofvaries with the solvent or solvent mixture and, in general, the moreclosely the solvent or solvent mixture approaches the desired balance ofpolar groups-and hydrocarbon constituents, the less the permissibleproportion of water to avoid the introduction of excessive gelling orinsolubility. small proportions of water below the limits above setforth may be advantageous. The maximum permissible proportion may bereadily determined experimentally in each instance and in many cases maybe as low as 2 or 3%.

By the term substantially anhydrous, in connection with solvents orsolvent mixtures, as used herein, I mean having insufiicient water inthe solvent or solvent mixture to disturb the balance thereof andintroduce excessive gelling or insolubility, and having in no case morethan 5% water.

By the use of anhydrous or substantially anhydrous solvents or solventmixtures in accordance with my invention, I am thus enabled to preparesubstantially non-aqueous zein solutions and coating compositions whichcontain no added water, or only slight amounts thereof, not in excess of5% and, preferably, less. By virtue of this low added water content, thefield of applicability of the coating compositions and solutions inaccordance with my invention is materially widened beyond that of theaqueous coating compositions of the prior zein art. In addition, thefilms depositedfrom my coating compositions and solutions have none ofthe serious drawbacks as to brittleness, lack of luster and gloss andblooming and blushing tendencies of the films deposited from the aqueoussolutions or coating compositions of the prior art.

The quantity of anhydrous or substantially anhydrous solvents ormixtures of solvents necessary to prepare the desired solutions orcoating compositions in accordance with my invention may vary ratherwidely from about 2 to 20 or more and, preferably from about 2 to about9 or moreparts by weight of the solvent to 1 part by weight of the zein.In most instances, 3 to 5 parts by weight of the solvent to one part byweight of the zein has been found sufficient to dissolve the zein andform the desired stable solutions or coating compositions. The viscosityand gelling tendencies of the solutions or coating composi- Since ethylalcohol In some cases tions prepared in accordance with my invention areat least in part dependent on the proportion of solvent used.

The coating compositions embodying my inven-" tion having the unusualproperties, particularly when heated, of being able to give up theirsolvent or solvents readily when applied to any surface to quickly andreadily form tough, flexible, non-tacky, hard and generally transparentfilms even when retaining some solvent. The films deposited from coatingcompositions in accordance with my invention are very strong and haveunusual adherent properties. In these coating compositions the filmforming properties thereof compositions in accordance with my inventionwill produce non-blushing coatings on drying, without the aid ofsupplementary anti-blushing agents as in the prior art.

The coating compositions in accordance with my invention may be appliedto any surface and they may be used for coating, sizing, or impregnatingany material, such as paper, textiles, wood, wood pulp and the like.When coated on paper, Cellophane, glass and the like, a film is formedalmost immediately which possesses the film characteristics set forthabove. Since these coating compositions have decided adhesiveproperties, they may be used either per se or in combination with othermaterials for uniting or laminating paper, cloth, wood, glass, felt,Cellophane, metals and metal foils and the like.

The characteristics of the coating compositions in accordance with myinvention, and hence of the ultimate films formed therefrom, can bealtered at will and as desired by the inclusion of diluents, modifiers,plasticizers, resins, cellulose derivatives, fillers and the like, allas set forth in my prior application Serial No. 295,919.

I claim:

1. A substantially non-aqueous liquid coating composition comprising 1part by weight of zein and at least about 2 parts by weight of analcohol ether solvent for the zein, said solvent and said compositioncontaining not in excess of about 5% of added water and said compositionbeing stable against separation of the zein at temperatures of 70 F.

2. A substantially non-aqueous liquid coating composition comprising 1part by weight of zein and at least about 2 parts by weight of ethyleneglycol-monomethyl ether, said solvent and said composition containingnot in excess of about 5% of added water and said composition beingstable against separation of the zein at temperatures of 70 F.

3.- A substantially non-aqueous liquid coating composition comprising 1part by weight of zein and at least about 2 parts by weight ofdiethylene glycol monomethyl ether, said solvent and said compositioncontaining not in excess of about 5% of added water and said compositionbeing stable against separation 01 the zein at temperatures of 4. Asubstantially non-aqueous liquid coating composition comprising 1 partby weight 01' zein andat least about 2 parts by weight of ethyleneglycol monoethyl ether, said solvent and said composition containing notin excess of about 5% of added water and said composition being stableagainst separation of the zein at temperatures of 70 F.

5. A substantially non-aqueous liquid coating composition "comprising. asubstantially nonaqueous solution of zein and a resin, said zeinsolution comprising 1 part by weight of zein and at least about 2 partsby weight of ethylene glycol monoethyl ether, said solvent and saidcomposition containing not in excess of about 5% of added water and saidcomposition being stable against separation of the zein at temperaturesof 70 F.

6. A substantially non-aqueous liquid coating composition comprising asolution of zein and a resin, said solution comprising zein and asubstantially anhydrous solvent for the zein having I a proportion ofpolar to non-polar radicals which lies within a range extending betweenthe limits of the proportion of polar to non-polar radicals of methanoland the proportion of polar -to non-polar radicals of ethanol, saidsolvent and said composition containing not in excess of 5% of addedwater and said composition being stable against separation of the zeinat temperatures of 70 F. and being relatively non-gelling.

7. A substantially non-aqueous liquid coating composition comprlsing'asolution of a prolamin and a resin, said solution comprising a prolaminand a substantially anhydrous solvent for the prolamin having aproportion of polar to nonpolar radicals which lies within a rangeextending between the limits of the proportion of polar to non-polarradicals of methanol and the proportion of polar to non-polar radicalsof ethanol, said solvent and said composition containing not in excessof 5% of added water and said composition being stable againstseparation of the prolamin at temperatures of 70 F. and being relativelynon-gelling.

8. A substantially non-aqueous liquid coating composition comprisingzein and a substantially anhydrous solvent for the zein having a balanceof polar to non-polar radicals approaching that of ethanol and borderinga range which ex-' tends between the proportion of polar to nonpolarradicals of methanol and the proportion of polar to non-polar radicalsof ethanol, said solvent and said composition containing not in excessof 5% of added water and said composition being stable againstseparation of the zein at temperatures of 70 F. and being relativelynon-gelling.

9. A substantially non-aqueous liquid coating composition comprising 1part by weight of zein, at least about 2 parts by weight of asubstantially neutral hydroxylated organic solvent for the zein otherthan ethyl alcohol and a resin, said solvent and said compositioncontaining not in excess of about 5% of added water and said compositionbeing stable against separation of the zein at temperatures of 70 F.

ROY E. COLEMAN.

